The present invention relates to a telecommunications network provisioned with a distributed restoration algorithm (DRA) and, more particularly, to ascertaining the quality of certain links cross-connecting adjacent nodes in the network.
In a telecommunications network provisioned with a distributed restoration algorithm (DRA), when a fault occurs at any one of the links of the network, the DRA algorithm within each node would try to find an alternate route that circumvents the failed link, or node, by using the spare links that interconnect the nodes of the network. Normally, to find an alternate path or paths, the DRA process first determines the availability of any spare links after the failure is detected. As spare links that form the alternate paths are found, all of those spare links are presumed to be equivalents in terms of their reliability.
When there is a failure, the DRA process has to act quickly, so as to minimize the disruption to the network. Accordingly, the DRA process usually does not have the time to monitor the integrity of the spare links for any length of time before the disrupted traffic is switched onto the available spare links that form the alternate route(s). As a consequence, some of the spare links that the DRA process selects may fail subsequent to the switch. Such subsequent failure is undesirable insofar as it compounds the disruptive effects of a failure.
Therefore, a method is required for a DRA process to readily identify any links that are seemingly intact but are susceptible to failure shortly after the restoration process, i.e., the switching of the disrupted traffic onto the spare link, is completed. By being able to identify those links that are susceptible to failure shortly after restoration, i.e., low quality links, the DRA process can make a better selection of the alternate paths for rerouting the disrupted traffic.
Some known methods are based partly on a determination of whether a spare link is part of a span where other links have failed. The assumption of these methods is that within a span where some links have failed, the failure of the remaining links is also likely. Such a characterization relies mostly upon identifying the custodial nodes adjacent a failed span so that any seemingly intact spare link(s) between the custodial nodes may be assigned a lower quality rating. Thus, each node in a network that has observed a failed link would emanate a message along all of the spare links. But there is no way for a node to know which spare links corresponds to a given working link. In other words, there is no communications means within the working links to allow for node identification. Thus, the message is sent out indiscriminately along all spare links rather than only the selected few where failure had actually occurred. Consequently, this technique gives rise to inefficiency in communication.
A method is therefore required for more reliably identifying low quality spare links and, more specifically, for identifying the particular pair of custodial nodes that are associated with each span failure so that the proper quality value may be assigned to those spare links associated with the failed span.
When a portion of a path through a telecommunications network is interrupted due to a failure of the link(s) along the path, the failure is detected by the nodes on either side of the failure. The detecting nodes adjacent the failure, i.e., the custodial nodes, each independently output a special message towards the respective end nodes of the failed path. The special message includes, among other things, information about which portion, i.e. the links, of the failed path, remain functional or intact. This information is provided to the various nodes of the network using the functioning or intact links of the path.
When each end node of the failed path receives the special message, it extracts the identity of the custodial node from the route information portion of the message. Each end node, in turn, informs the other end node of the location of the custodial node from which the special message was received by means of a data communications network independent of the telecommunications network, such as a wide area network (WAN). Then the end nodes, collectively or individually, communicate over the independent communications network custodial node information to each custodial node of the failed link to inform that custodial node of the identity of the other custodial node. With each custodial node cognizant of its opposing custodial node, any failed link that cross-connects custodial nodes can be identified. The quality of such identified link is then presumed to be lower than those links that are not associated with both custodial nodes. This presumption is based on the fact that those functional links that cross-connect the custodial nodes of the failed link may very well be rendered non-functional shortly because whatever caused the failure to occur at the failed link will most likely also affect those remaining functional links.
An objective of the present invention is to eliminate the propagation of unnecessary xe2x80x9cI am a custodial nodexe2x80x9d messages to the various nodes of the network by providing to each of the custodial nodes of a failed link the knowledge of which of its adjacent nodes is the other custodial node.
It is another objective of the present invention to readily determine the quality of the links interconnecting the nodes of the network by readily segregating those functional links that cross-connect the custodial nodes of a failed link from other functional links.
It is moreover another objective of the present invention to more accurately determine which spare links lie along a failed link and, more particularly, which functional links are associated with the failed link and should therefore be considered to be of lower quality.